The microtiter plate has become a standard tool in analytical research and clinical diagnostic testing laboratories. A very common usage is in the enzyme-linked immunosorbent assay ELISA, the basis of most modern medical diagnostic testing in humans and animals. Other uses include growth and analysis of bacterial or fungi cultures, DNA purification, soil analysis, fermentation studies, and other small-scale bio-chemical processes. Microtiter plates enable the testing of many small volume samples at one time, shortening the analysis process time and greatly reducing the amount of sample required. The later is particularly critical as the cost of the sample materials is often quite high.
Typically, microtiter plates are used in automated testing equipment, where robotic arms place microtiter plates onto a flat stage. Another robot then dispenses small quantities of one or both of chemicals and cultures which will undergo testing, into each small well. It is common for each well to have slightly different mixtures. The small size of each well makes it conducive to have precise alignment of the microtiter plate to the robotic arms.
In many of the microtiter plate uses, it is desirable to control the temperature of the sample as the contents are either temperature sensitive, or in the case of bacterial or fungi cultures, grow at rates that change exponentially with temperature. Various methods for controlling microtiter plate temperature have been tried, such as immersing the microtiter plate in a circulating fluid, blowing a heated or cooled air over the microtiter plate surface, and placing it on a heated or cooled plate.
The first two methods have serious drawbacks. Immersing a microtiter plate in a circulating fluid is problematic for two reasons: first, the microtiter plates are made from low density materials and tend to float, and second, the coolant can get into the wells, contaminating the sample. Blowing air over the microtiter plate surface has similar problems with potential contamination and, due to the low thermal mass of air, precise temperature control over the microtiter plate surface is nearly impossible.
It has been known to insert a microtiter plate into a heated or cooled cold plate to solve these problems, but a new problem arises when the microtiter plate temperature must be maintained below the ambient dew point: condensation of moisture. Minimizing condensation requires insulating all but the top surface of the cold plate with a plastic or foam insulation, which in turn creates still a new problem: alignment of the microtiter plate. It is very difficult to precisely machine or cut plastic or foam insulation. As a result, it is very difficult to maintain an insulated cold plate's precise thickness and a parallelism between a plastic base and metallic top surface. This imprecision leads to positional variation across the cold plate surface relative to the cold plate's mounting base which in turn creates problems for alignment of robotic arms that commonly load the microtiter plates onto the cold plate.